The proposed work is directed to the evaluation of the thermodynamics of mono and bimolecular (elementary) events in enzyme catalysis. Systems to be studied include the interactions of strained cyclic esters and transition state analogs with serine proteases. The ultimate objectives are to evaluate part processes which compose certain elementary steps in enzyme catalytic reactions. Among the part processes of interest are enzyme conformation changes and covalent bond breaking and making within the enzyme active site.